Switching techniques and devices

ABSTRACT

A method and a device for introducing or removing an electrical signal through rapid switching of an analog switch between the on and off conditions with the switch remaining in one condition longer initially, and then progressively less in the one condition and longer in the other until the transfer has been completed. The magnitude of a repetitive waveform is compared with the magnitude of a ramp waveform to generate the control signal which determines the interval that the switch remains in a given condition. By controlling the on and off condition of a second switch in opposition to the first switch and by combining the outputs of the switches, a smooth transition between two control signals is achieved. The method and the device are applied to an elevator speed control system wherein transition is provided between several signal sources.

United States Patent Szabo et al.

[ 1 Mar. 28, 1972 SWITCHING TECHNIQUES AND Primary Examiner-Bemard A.Gilheany DEVICES Assistant ExaminerW. E. Duncanson, Jr.

--.T.t ,.L. d dR'hdV. [72] Inventors: Andras I. Szabo, Export; CharlesL. Wlnafggzg S C Free man an at ltler, Pittsburgh, both of Pa. [73].Assignee: Westinghouse Electric Corporation, Pitt- ABSTRACT sburgh' Amethod and a device for introducing or removing an electri- [22] Filed:Feb. 24, 1970 cal signal through rapid switching of an analog switchbetween [21] APPLNO': 13'660 the on and off conditions with the switchremaining in one condition longer initially, and then progressively lcssm the one condition and longer in the other until the transfer has--187/29 R.3 7/243.3 been completed. The magnitude of a repetitivewaveform is 328/104. 328/154 compared with the magnitude of a rampwaveform to generate [5|] lnt.Cl. ..H03lt 17/26 Conn-cl signal whichdflcrmines he imcrval that he [58] new 87/29; 307/243; 328/104 154;switch remains in a given condition. By controlling the on and Ina/293'345'599 off condition of a second switch in opposition to the firstswitch and by combining the outputs of the switches. a smooth [56]Rdercnm cued transition between two control signals is achieved. The

UNTED STATES PATENTS method and the device are applied to an elevatorspeed control system wherein transition IS provided between several 2.92l MOl'flSOn 3 l X signal su cs 3.5l6,5i8 6/l970 Krauer et al... ..l87/2915 Claims, 8 Drawing Figures i A ANALOG SiGNALl P V SWITCH 8 COMPARATORB 7 IO TRANSITION P5 SIGNAL 2 hiifi SIGNAL 2 PATENTEUIIIIQII 1972 SH'IIU1 BF 2 45] 3 2 a COMPARATOR TRANSITION 5 2 SIGNAL LEV ISVJ ANALOGSIGNAL! SWITCH COMPARATOR B TRANSITION av 9 SIGNAL v.

I 2 FIG. 2.

ANALOG SIGNALZ", r SWITCH 1O '1 E I s R FIG. 4A.

CLOSED 1 1 L d FIG. 4B. OPEN CLOSED P 1 FIG 4C OPEN Li L,

O r FIG. 40.

I SIGNAL 2 FIG. 4E.

SWITCH #2 CLOSED SWITCH #l CLOSED sIG-AI I SWITCHING TECHNIQUES ANDDEVICES BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to switching devices and techniques and moreparticularly to such devices and techniques for use in switching controlsignals wherein the application of a signal or the switching betweensignal sources must be smooth.

2. Prior Art With conventional switching techniques wherein a switch isoperated from the closed to the open position or vice versa in one step,the signal being switched is introduced or removed rapidly. Thetransients introduced by such switching when utilized in controlcircuits can induce undesirable response in the system being controlled.As a result, it has become the practice, in some instances, to introducesuch signals through filters. However, this technique has thedisadvantage that since the filter remains in the circuit, it can dampenthe desired response of the system to variations in the control signalonce it has been switched on. It is also possible to Introduce such asignal at a controlled rate through the use of a potentiometer, however.this has the disadvantage of requiring a mechanism for driving the wiperarm with the accompanying problems of mechanical wear.

Smooth switching is also a problem in systems wherein a transfer is madefrom one signal source to another, as from a coarse control signal to afine control signal or vice versa. Such problems arise in the speedcontrol systems for elevators. For instance, very often the speedcontrol signal for acceleration and constant speed is generated as afunction of time, while the speed control signal for the decelerationphase is controlled as a function of the distance remaining to the pointat which the car is to stop. In some instances, a third signal generatoris utilized to generate a very accurate speed control signal over thelast few inches of travel to assure accurate landings. The problem ofproviding smooth transition from one signal source to another isparticularly acute in the elevator field since passengers arefreestanding on a moving platform. One approach to this problem has beento attempt to match the magnitudes of the control signals so that theywill be approximately equal at the point when the switchover shouldoccur. However, when the control signal is used for a speed control. notonly the magnitudes of the signal must be approximately equal, but theslope, or rate of change of the control signals, must also match orapproximate each other at the time of switchover or undesirabletransient response will occur.

SUMMARY OF THE INVENTION tion controlled bytthetoetptttofmccomperauor-avhichlhastoaeror another condition depending uponwhether the instantaneous value of a ramp function is more than or lessthan the instantaneous value of a repetitive function, preferably asawtooth function. The minimum value of the ramp function is made lessthan the minimum value of the sawtooth function while the maximum valueof the ramp function is made more than the sawtooth function so that theoutput of the comparator changes. and therefore the condition of theswitch changes, only when the ramp function is transferring between itspeak values.

The transition time of the ramp function determines the transfer timefrom the full on to the full off condition of the switch and thereforeestablishes the rate at which the signal is applied or removed. Sincethe components which control this transfer time are in the controlcircuit for the switch and not in the circuit being switched, they donot affect the response of switched as would a filter. Consequently, thetransfer time can be made reasonably slow without affecting the dynamicresponse of the system to the control signal once it is switched on.

The frequency of the sawtooth function determines the rate at which theswitch is operated between the off and on conditions. If this rate ismade rapid with respect to the response time of the system beingcontrolled by the switched signal, the effect will be a smoothapplication or removal of the signal with the rate determined by thetransition time of the ramp.

By connecting a second switch so that it is switched from the off to theon condition in opposition to the first switch in response to the outputof the comparator, and by combining the outputs of the two switches in asumming circuit, the invention can be used for switching smoothly fromone control signal to another. Again the transfer time will bedetermined by the transition time of the time ramp function and the rateof repetitive switching will be determined by the frequency of thesawtooth waveform. The second switch is operated in opposition to thefirst switch by interposing a conventional NOT logic circuit between thecomparator and the second switch. With this configuration, one switchwill be on I00 percent of the time initially while the other one will beoff I00 percent of the time. As the transition occurs, the relativepercentage of contribution of the two signals will change progressivelyuntil the one switch will be off I00 percent of the time while the otherswitch will be on I00 percent of the time.

In the preferred embodiment of the invention, the ramp function iscontrolled as a function of time; however, the value of this waveformcould be controlled as a function of another variable such as theposition of the body being controlled.

The invention can also be applied to systems wherein a control signal isselected from more than among two signal sources. As applied to anelevator system wherein a speed control signal is selected from amongthree signals, only one sawtooth generator is required while rampfunction generators for each pair of signal sources between which atransfer is desired are required. Separate comparators are required forcomparing the value of the sawtooth waveform with the waveform of eachof the ramp function generators. Gate circuits operated by a supervisorycontrol serve to insure that operation of a switch controlling a signalsource common to two transfers is controlled by the output of the propercomparator.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a block diagram of a basicembodiment of the invention;

FIG. 2 is a block diagram of another embodiment of the invention adaptedfor use in switching between two signal sources;

FIG. 3 is a block diagram of yet another embodiment of the inventionadapted for use in an elevator speed control system;

FIGS. 4A through E illustrate waveforms appearing at- We:mihthrnssgifl'i.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. I illustrates theinvention as employed in a simple switching operation to control thecircuit between the terminals A and B. The device is composed of ananalog switch I interposed in the circuit between these terminals. Ananalog switch is a conventional type of a two condition switch whichopens the circuit between terminals A and B in one condition andprovides a short circuit so that the signal appearing at the terminal Aappears at the terminal 8 when the switch is in the closed condition.Although the switch could be of the electromechanical solenoid type,preferably the switch is a solid state switching device due to the rapidrepetitive switching desired.

Solid state switches which are responsive to a digital control signalapplied to a control Input 2 are well known. An exemthe control systemto the transients in the control signal being plary solid state switchis shown in FIG. I within the dashed line. Base electrodes l3 and B, ofa field effect transistor Q are connected between the terminals A and B.A resistor R is connected between B, and the gate electrode, G, of 0..The gate electrode is also connected to the collector of an NPN-transistor 0,. The emitter of Q, is energized by a v. DC source whilethe base of(), is connected to a l 2 v. DC source through resistor R,The control input 2 is connected directly to the base of 0,.

With no signal applied to the control input 2 of the switch 1. thetransistor Q, will conduct. The current thus drawn through resistor Rwill lower the voltage on the gate G of transistor 0,. to hold Q, cutoff and the switch I will therefore be in the open condition. When asignal which lowers the potential of the base ofQ, below -l5 v. DC isapplied to the control input 2. 0 is cut off and the potential on thegate G of transistor 0, will rise so that Q will be turned on. With Qconducting the switch I is in the closed condition. it will beappreciated that if no control signal is applied to the control input 2.switch I will be biased to the open condition.

The control signal for the analog switch is generated by a comparator 3which has one output when the instantaneous value of a signal applied toan input 4 exceeds the instantaneous value of signal applied in input 5and a second output when the signal applied at the input 5 exceeds thevalue of the signal applied at the input 4. Comparators displaying suchcharacteristics, and having as one output a zero voltage signal andhaving as a second output a signal of a fixed magnitude are well ltnown.Signals to be compared by the comparator 3 are supplied by a firstfunction generator 7 which generates a repetitive waveform. preferably asawtooth waveform, and a second function generator 8 which preferablygenerates a ramp function. The sawtooth function generator 7 can operatecontinuously while the ramp function generator 8 maintains an output ofone peak value or the other until triggered by a transition signal.whereupon the ramp function transitions to the opposite pealt value.Function generators of these general characteristics are also wellknown.

Reference to FIG. 4 will aid in understanding the operation of thedevice of FIG. 1. Assuming that initially the ramp function R is at itsminimum value which is less than the minimum value of the sawtoothfunction S (see FIG. 4A). the signal appearing at input 4 of thecomparator will exceed the signal applied to the input 5 so that theoutput of the comparator will remain constant. If it is assumed thatthis output when applied to the control input 2 of the analog switch Iis such as to maintain the switch in the open circuit state, thecondition of the switch would be as shown in FIG. 48. Suppose now that atransition signal is applied to the ramp generator 8 to cause thegenei'ation of a ramp function. As the ramp function R begins to rise invalue at I the output of the comparator. and therefore the condition ofthe analog switch. remains constant since the instantaneous value of thesawtooth waveform S continues to exceed the value of the ramp function.However, at the completion of the second cycle of the sawtooth waveformshown in FIG. 4A, the instantaneous value of the ramp function R exceedsthat of the sawtooth wavefonn. Since the value of the signal applied tothe input 5 of the comparator now exceeds the value of the signalapplied to the input 4. the output of the comparator 3 switches therebycausing the operation of the analog switch 1 to the closed condition.Since the value of the sawtooth waveform soon exceeds the value of theramp function again. the output of the comparator. and therefore thecondition of the analog switch. quickly switch back to their originalstates. it can be seen therefore, that any signal applied to theterminal A of the device of FIG. 1 appears at the terminal B for only avery short interval. ltcan be appreciated from FIGS. 4A and 48, however.that the value of the ramp function exceeds that of the sawtoothfimction for a longer interval after the completion of the third cycleof the sawtooth waveform. Consequently, the analog switch 1 remainsclosed for a longer interval on this cycle. it is clear from FlGS. 4Aand B that the ramp function R remains larger than the sawtooth function5 for longer intervals on successive cycles of the sawtooth function sothat the switch remains in a closed position for successively longerintervals until after the seventh cycle of the sawtooth function theswitch remains permanently in the closed condition.

The relationship between the instantaneous value of the sawtoothfunction and the ramp function in FIGS. 4A'and 4B was selected for thesake of clarity. in actuality the slope of the ramp function R would bemuch less so that hundreds of incremental switching operations wouldoccur as the ramp function transitions from its minimum to its maximumvalue. For instance, it has been found that when the device is appliedto a speed control system for an elevator as described in detail below,satisfactory switching is achieved by utilizing a ramp function whichtransitions from one peak to the other in three tenths of a second and asawtooth function which has a period of l millisecond. With theseparameters, nearly 300 switching operations will occur as the analogswitch I is progressively switched from being predominantly in the opencircuit condition to being predominantly in the closed circuitcondition. The exact figure will be somewhat less titan this asdetermined by the amount by which the peak values of the ramp functionexceed the peak values of the sawtooth function thereby eliminating someof the switching operations while the ramp function is near its peakvalues. it can be appreciated, therefore. that the signal appearing atterminal B will have a l kilocycle component during the switchingoperation. in many applications the dynamics of the system will be suchthat this one kilocycle transient will be automatically dampened.However. if desired, a low pass filter 9 can be inserted between theanalog switch and the terminal B to eliminate this component.

The transition time of the ramp function however. is the operativefactor which detennines the rate at which the analog switch is operatedfrom its predominantly closed to its predominantly open condition.Referring to FIG. 40. if a continuous signal shown by the dotted line ais present at the input terminal A, the signal appearing at the terminal8 is represented by the solid line b. Again this is an idealizedrepresentation which illustrates the theoretical signal which wouldappear at the terminal 8. In reality, the signal at terminal B willapproach this signal as the frequency of the sawtooth waveform isincreased with respect to the transition time of the ramp function. itcan be seen however. that the signal at terminal 8 will be zero untilthe ramp function begins to exceed the value of the sawtooth functionduring part of the cycle of the sawtooth function. it can be appreciatedthen that the signal applied to the tenninal A appears at the terminal Bsmoothly over a period of time determined by the transition time of theramp function. As was mentioned previously. this transition time in oneapplication has been set at three tenths of a second. It will be notedhowever. that once the switching has been completed there is norestriction in the circuit between the terminals A and B toinhibit theresponse of a component connected to the terminal 8 to transient signalsapplied to the terminal A.

in other words. through the utilization of this invention. the signalappearing at A can be applied to the system connected to the terminal Bat a rate which is compatible with the dynamic characteristics of theload but yet it does not interpose a reduction in the response time ofthe system. This should be contrasted with the prior art procedure ofinterposing a filter in series with a switching circuit to dampen theresponse of the system to the switching operation. lf the filter is todampen the response of the system to the transient caused by theswitching operation it will also dampen the response of the system totransients in the control signal applied to the terminal A. According tothis invention however. the components which control the switchingoperation are in control circuit for the analog switch and not in theload circuit, therefore once the switching operation is completed theydo not inhibit the response of the load to transients in the signalapplied to the terminal A. it should be remembered that the low passfilter 9 which may be interposed in the load circuit will pass allfrequencies occurring in the normal transients of the control signalapplied to the terminal A. it merely eliminates the high frequencytransients caused by the switching operation itself and, as wasmentioned, if the cutoff frequency of the system is low enough, thisfilter is not necessary.

it is apparent that the signal applied to the terminal A can be removedfrom terminal B through the reverse switching process by a transition ofthe ramp waveform back to its original value. This could be accomplishedby the removal of the transition signal from the ramp function generator8. During this transition, analog switch 1 would initially predominantlyremain in the closed condition and then progressively less in the closedcondition and more in the open condition during successive cycles of thesawtooth function until the value of the ramp function dropped below theminimum value of the sawtooth function so that the switch would remainin the open circuit condition. it can be appreciated that although asawtooth function and a ramp function were selected to provide a lineartransition in the switching operation, other repetitive waveforms can besubstituted for the sawtooth function and another transition functioncould be substituted for the ramp function.

FIG. 2 illustrates the application of the invention to a dual switchingoperation for switching between two signal sources. The two signalsources are connected to the terminals A and A. Analog switch l isinterposed between terminal A and the output tenninal B while the analogswitch I 2 is interposed between the terminal A and the output terminal8. The analog switch ll is controlled by the signal applied to itscontrol terminal 2 in a manner similar to that described for the controlof the analog switch in the device of FIG. l. in other words, analogswitch 01 is controlled by the output of the comparator 3 whichgenerates a digital signal having a value of either zero or onedepending upon whether the value of a sawtooth waveforrn applied toinput terminal 4 of the comparator is larger than, or less than, thevalue of a ramp function applied to the input terminal 5 of thecomparator.

For illustrative purposes, it will be assumed that the analog switch I lof HO. 2 will respond to the relative values of the ramp function andthe sawtooth function as did the analog switch of FIG. I so that itscondition is represented by the FIGS. 4A and 4B. The additional analogswitch 02 is also operated between its open and closed condition by acontrol signal applied to its control terminal 2'. The control terminal2' is connected to the output of the comparator 3 through a conventionalNOT-logic circuit ill. The conventional NOT circuit reverses the digitalsignal applied to its input. For instance, if a ONE is applied to theinput of the NOT element a ZERO output is produced and vice versa.Therefore, the control signal applied to the control input 2' of analogswitch 0 2 will at all times be opposite to the control signal appliedto the control terminal 2 of the analog switch 0 1. it is clear thenthat when the analog switch 0 l is in closed condition analog switch I2, which is identical to the analog switch 0 I, will be in the opencondition and vice versa.

Since it was assumed that the condition of analog switch 0 l withrespect to the relative values of the ramp function and the sawtoothfunction would be illustrated by FIG. 4B, the operation of the analogswitch 4 2 with respect to the ramp function and sawtooth function isillustrated by H0. 40. it will be noted that for the assumed conditionsanalog switch 0 2 is initially predominantly in the closed condition andprogressively remains a shorter interval in the closed condition andlonger in the open condition through successive cycles of the sawtoothfunction. it can be appreciated then that only one switch at a time isin the closed condition so that either the signal applied to theterminal A or A alone is passed to the terminal 8. A summing circuit llconnected to the two analog switches supplies the combined signal to theterminal B. The summing circuit can be a conventional operationalamplifier which may also be modified to act as a low pass filter ifnecessary. Alternatively, the summing circuit could be replaced by avoltale follower circuit.

' FIG. 45 illustrates the operation of the circuit of FIG. 2. it will beassumed that the signal I 1 shown as a dashed line is applied toterminal A and that signal I 2 illustrated as a dotted line is appliedto the terminal A'. The solid line represents the resultant signalappearing at the terminal B assuming that the summing circuit ll doesnot operate as a low pass filter. The dash dot line curving between thesignal 0 2 and signal 01 represents the effective value of the signalappearing at the terminal B assuming that the summing circuit ll alsoacts as a low pass filter. Under the assumed conditions, when the rampfunction R of FIG. 4A is smaller in value than the sawtooth function 8so that the analog switch l is opened and the analog switch I 2 isclosed, the signal I 2 appears at the output terminal B. At thebeginning of the third ii- I lustrated cycle of the sawtooth waveformwhen the ramp function momentarily exceeds the value of the sawtoothfunction, analog switch 1 will close while the analog switch 02 willopen momentarily thereby causing the signal which appears at the outputterminal 8 to drop to the instantaneous value of the signal 1. Withsuccessive cycles of the sawtooth function, it can be seen that thesignal ll progressively appears longer at the output terminal 8 than thesignal 02 as the switch 0 l progressively remains longer in the closedcondition while the switch 02 remains progressively longer in the opencondition. it can be seen that alter the seventh illustrated cycle ofthe sawtooth waveform, the switch 0! remains closed while switch 02remains open so that signal 01 applied to the A- terminal of the deviceof FIG. 2 appears at the output terminal B continuously. Obviously theoutput of the device can be switched back to signal 0 l by causing theramp function to transition from its maximum value back to its minimumvalue. The filtered value of the signal appearing at the output terminalB of course will follow the dash dot line which represents a weightedaverage of the signals during the transition period.

FIG. 3 illustrates the application of the invention to an elevator speedcontrol system. in this system, elevator car 20 is suspended from acable 21 which passes over a sheave 22 and is connected to acounterweight 23. The car 20 is caused to travel up and down serving anumber of landings by a motor 24 which rotates the sheave 22 through ashaft 25. The shaft 25 also drives a floor selector 26. The floorselector is a device well ltnown in the elevator art which follows theposition of the car relative to the landings and cooperates with asupervisory control 27 to initiate the stopping of the elevator car asit approaches a floor at which service is desired. in many elevatorsystems the floor selector operates as a pattern generator whichdevelops a speed control signal as a function of the distance remainingto a floor at which the car is to stop.

it has been found that good results can be achieved by controlling thespeed of a car during acceleration as a function of time to providecomfortable and smooth acceleration for the passengers. Therefore, atime ramp generator 28, which is triggered by the supervisory controlsystem when the car is to start, can be utilized to generate a controlsignal for controlling the speed of the car during acceleration. it hasbecome common practice to utilize this ramp generator also to controlthe speed of the car during the constant speed phase. However, as thecar approaches a landing at which it is to stop, accurate landings withsmooth deceleration and no overshoot can be achieved by controlling thespeed of the car as a function of the distance remaining to be traveled.This signal is most often generated by pattern generator connected tothe floor selector. Due to the technical restrictions of size and cost,this signal produced by the pattern generator is a rough signal whichcontrols the car very well during the initial stages of deceleration.However, to assure precise landing without overshoot, it has becomewidespread to utilize a third signal generator to control the speed ofthe car precisely during the last critical inches of travel. A devicefor producing this fine signal is illustrated in US. Pat. No. 2,874,806.According to this system an electromagnetic transducer 29 connected tothe elevator car is activated as the car approaches a landing at whichit is to stop. Diamond shaped magnetic plates P. located adjacent eachlanding. vary the coupling between the poles of the transducer. Theinductor plates are so located with respect to the landings that a nullsignal is produced by the transducer when the car is exactly level withthe landing.

The speed of the car then is controlled by a signal developed either bya time ramp generator. at distance dependent pattern generator or alanding transducer depending upon the phase of the trip. The applicationof the selected signal to the motor control circuits is governed bythree analog switches similar to those discussed in connection withFIGS. 1 and 2. A time ramp generator which is controlled by asupervisory control system supplies a control signal during accelerationand at constant speed through the analog switch I]. The patterngenerator which supplies the signal to the motor control circuit duringthe deceleration phase is controlled by the analog switch 02. Thelanding transducer which supplies a control signal during the landingphase is rendered effective by analog switch 03. The output of theterminals of the three switches are connected to the summing and filtercircuits ll similar to that discussed in connection with FIG. 2 which inturn supplies the resultant control signal to the motor and controlcircuits 24.

The switching of analog switches O l and 2 is controlled by a circuitsimilar to that shown in H0. 2. The instantaneous magnitudes of asawtooth waveform generated by function generator 7 and of a rampfunction generated by function generator 8 determine the digital outputof a comparator 3. As in the circuit of FIG. 2. the output of thecomparator 3 is reversed by a NOT-circuit before being applied to thecontrol input of analog switch 2. The transition of the ramp function iscontrolled by a transition signal which is generated by the supervisorycontrol 27. in these respects this portion of the circuit of FIG. 3 isidentical to that of FIG. 2.

A second comparator 3 compares the instantaneous value of the sawtoothwavefonn 7 and a ramp function generated by an additional functiongenerator 8 to also control the switching of analog switch 0 2 inaddition to analog switch 0 3. A NOT-circuit l0 interposed between thecomparator and analog switch '3. assures that opposing control signalswill be applied to analog switch I 2 and analog switch 03 by thecomparator 3'. The function generator 8' is also controlled by atransition signal generated by the supervisory control 27.

In the circuits of FIG. 3. AND-gates 30 and 32 are interposed betweencomparators 3 and 3' and analog switches O l and I 2 respectively.Similarly AND-gates 3i and 33 are interposed between NOT-elements l0 and10' and analog switches 0 2 and O 3. All of these AND gates have twoinputs and a single output. These gates are the conventional AND logicgates which have a ONE output only when a signal is applied to both inuts. The second input to gates 30 and 31 is the signal A generated bythe supervisory control system 27. The second input to AND-gates 32 and33 is the signal LAND generated by the supervisory control system.Signals LAND and [AND are complementary signals in that when one ofthese signals is equal to ONE. the other one is equal to ZERO. it can beappreciated therefore that the output of only one AND circuit at a timecan be equal to ONE. For instance. if the signal LAND is equal to ONEthe signal LAND will be equal to ZERO and therefore the output ofAND-gates 32 and 33 cannot be equal to ONE regardless of the value ofthe other input. Since the second input to the AND-gate 3| is thereverse or the complement of the second signal applied to the ANDgate30. only one of these AND gates at a time will have both inputs equal toone. The signal LAND will be equal to ONE only during the landing phase.At all other times. the signal LAND will be equal to ONE.

A typical trip of an elevator would help in understanding the operationof the system shown in H6. 3. When the supervisory system indicates thatthe car should be started the signal LAND will be equal to ONE and thesignal LAND will be equal to ZERo. Under these conditions the output ofAND- sumed initially that each analog switch would be operated to theopen condition as long as a ZERO signal was applied to the controlinput. the analog switch I 3 will remain in the open circuit condition.The analog switch 02. however. may be controlled by the output of theAND-gate 31 even though the output of the AND-gate 32 is equal to ZERO.Let it be assumed further that the time ramp function produced by thefunction generator 8 is at its minimum value so that the value of thesawtooth function 7 exceeds the value of the ramp function. Therefore.the out ut of comparator 3 will be equal to ONE. Since the signal LA isalso equal to ONE. the signal supplied to the control input of analogswitch 0 l by the AND-gate 30 will be equal to ONE to operate the analogswitch 0 l to the closed position. Since a ZERO will be supplied to theAND-gate 31 by the NOT-element 10. a ZERO signal will be supplied to thecontrol input of analog switch a 2 by AND-gate 31. Therefore, with atriggering of the time ramp generator 28 by the supervisory control. thecontrol signal generated by this element will pass through the closedanalog switch 0 l and the sum'ming circuit ll to the motor and itscontrol 24.

Energization of the motor in turn will cause the car 20 to begin toaccelerate. Movement of the car will cause the floor selector to move insynchronism with it thereby following the position of the car. Movementof a car will also cause operation of the pattern generator whichgenerates a speed control signal as a function of distance required forthe car to come to a stop. however. this signal will not be applied tothe motor control circuit since the analog switch I 2 is held in theopen condition.

As the car approaches a floor at which the supervisory control systemindicates that the car is to stop. a transition signal will be suppliedto the ramp function generator 8. As the value of the ramp functionincreases. the output of the comparator 3 will reverse during thoseintervals when the value of the ramp function exceeds the instantaneousvalue of the sawtooth function. When the output of the comparator isequal to ZERO. analog switch 0 1 will be closed while the analog switch0 2 will be open due to the operation of the NOT circult 10. Asdescribed above. as the ramp function continues to build in value. theanalog switch 0 1 will progressively remain longer in the closedcondition as the analog switch 0 2 remains progressively longer in theopen condition until full transfer is achieved and the analog switch 01will remain.

closed while the analog switch 0 2 will remain open to apply thedistance dependent signal generated by the pattern generator to themotor control circuit through the summing circuit 11. 7

As the car approaches within a few'feet of the landing. the supervisorysystem will cause the LAND signal to go to ZERO thereby causing the LANDsignal to go to ONE. This will transfer control of the switching of theanalog switches to the output of the comparator 3 since. with the signalLAND equal to ZERO. the outputs of AND-elements 30 and 31 are clamped atZERO. it will be assumed that at this point. with the output of thefunction generator 8' at its minimum value. the output of comparator 3'will be equal to one to maintain the analog switch 0 2 in the closedcondition so that the control signal generated by the pattern generatorwill be continuously applied to the motor control circuit 24. At thistime. the supervisory controlsystem will supply a transition signal tothe function generator 8 to initiate a transfer from the patterngenerator to the landing transducer. During those initial periods whenthe instantaneous value of the function generator exceeds that of thesawtooth function. the output of the comparator 3 will go to ZEROthereby switching analog switch 0 2 to the open condition and analogswitch I 3 to the closed condition. in a manner which should be evidentat this point. the signal generated by the pattern generator will besmoothly replaced by the signal generated by the landing transducer.

it can be seen from the above description that the gates 31 circuits 32and 33 will be clamped at ZERO. Since it was asand 32 are essential forselecting which comparator will control the operation of analog switch I2. Considering that the initial states of the function generators 8 and8' are properly selected, the LAND inputs to the AND-gates 30 and 31 arenot essential but are useful in providing backup protection should amalfunction occur.

it is evident from FIG. 3 that additional switches can be controlled byadding additional sets of comparators and ramp function generators. Thesame or a separate sawtooth function generator 7 can be utilized foreach stage. Of course the proper gating signals for the AND gates mustbe supplied to insure the selective control of the individual analogswitches.

it is to be understood that the invention is not to be restricted to theembodiments specifically disclosed since it is evident that anyvariations fully within the scope of the invention could be made.

We claim as our invention:

l. A switching device comprising a switch having an input terminal andan output terminal. said switch being operative between a firstcondition wherein a circuit is completed between the input terminal andthe output terminal and a second condition wherein no circuit iscompleted between the terminals. and control means for operating saidswitch between said first and second conditions including meansoperative to rapidly and repetitively operate the switch between saidfirst and second conditions with said switch initially remaining in onecondition longer than the other and then progressively less in the onecondition and longer in the 7 other condition until the switch remainsin the other condition substantially continuously.

2. The device of claim l including a summing circuit operative toproduce an output signal which is a combination of the signals appliedto the summing circuit. a first signal source connected to said summingcircuit. a second signal source connected to the input of said switchand means connecting the output of said switch to said summing circuitwhereby the signal generated by the second signal source can graduallybe added to or removed from the signal appearing at the output of thesumming circuit through the operation of said control means to operatesaid switch from being predominantly in one condition to beingpredominantly in the other condition.

3. The device of clatm I wherein said control means comprises a firstfunction generator operative to generate a repetitive signal. a secondfunction generator operative to generate a second signal having a timeconstant which exceeds the period of oscillation of said first signal.and a comparator for comparing the instantaneous values of the signalsgenerated by said function generators and having a first output when theinstantaneous value of a first one of said signals exceeds theinstantaneous value of the other and having a second output when theinstantaneous value of the other signal exceeds that of said one signal.said switch being operative to one condition in response to the firstoutput of said comparator and operative to said other condition inresponse to said second output.

4. The device of claim 3 wherein a signal generated by said firstfunction generator is substantially a sawtooth signal wherein thesignals generated by the second function generator is substantially aramp function. the minimum value of said ramp function being less thanthe minimum value of said sawtooth function while the maximum value ofthe ramp fimction exceeds that of said sawtooth function whereby theoutput of the comparator and therefore the condition of the switch willremain constant except while said ramp function generator istransitioning between its peak values.

5. The device of claim 1 including a second switch which is operativebetween a first condition wherein a circuit is completed between aninput terminal and an output terminal and a second condition wherein nocircuit is completed between the terminals, and wherein the controlmeans includcs coupling means operative to operate said second switchbetween said first and second conditions in opposition to the operationof said first switch between said'first and second conditions whereby assaid first switch is operated from being predominantly in said onecondition to being predominantly in the other condition. said secondswitch is operated from being predominantly in said other condition tobeing predominantly in said one condition.

6. The device of claim 5 wherein said control means comprises a firstfunction generator operative to generate the repetitive waveform. asecond function generator operative to generate a second waveform havinga time constant which exceeds the period of oscillation of said firstwaveform, and a comparator for comparing the instantaneous values of thefirst and second waveforms and having a first output when theinstantaneous value of one waveform exceeds that of said other waveformand having a second output when the instantaneous value of said otherwaveform exceeds that of said one waveform. said first switch beingoperative to said first condition in response to one output of saidcomparator and being operative to said second condition in response tothe other output of said comparator while said coupling means operatessaid second switch to said second condition in response to said oneoutput of said comparator and operates it to said first condition inresponse to the other output of said comparator.

7. The device of claim 6 adapted for use in a control system wherein thesecond waveform is essentially a ramp function with a minimum valuewhich is less than the minimum value of said repetitive waveform and amaximum value which exceeds the maximum value of the repetitive waveformand including a first control signal source connected to the inputterminal of said first switch. a second control signal source connectedto the input terminal of said second switch. and a summing circuitconnected to the outputs of said switches whereby the control signalappearing at the output of the summing circuit is one control signal orthe other while the ramp function is at its maximum or minimum value andis progressively switched from one control signal to the other as theramp function transitions from one peak value to the other.

8. The combination of claim 7 including a third switch operative betweena first condition wherein a circuit is completed between an inputterminal and an output terminal and a second condition wherein nocircuit is completed between the tenninals. a third control signalsource connected to the input of said third switch the output of saidthird switch being connected to the summing circuit. an additionalsecond function generator operative to generate a waveform having a timeconstant which exceeds the period of oscillation of said first waveform.an additional comparator connected to the first htnction generator andthe additional second function generator and having a first output whenthe value of one of these waveforms exceeds that of the other and havinga second output when the value of the other waveform exceeds that ofsaid one waveform. the condition of said second and third switches beingresponsive to the output of said additional comparator. additionalcoupling means for operating said second and third switches inopposition to each other in response to the output of said additionalcomparator and actuating means operative to selectively actuate aselected second function generator to initiate a switching from onecontrol signal to another.

9. The combination of claim 8 including gates between the comparatorsand the respective switches to which they are connected. said actuatingmeans also including means for actuating said gates to control theresponse of said switches to the outputs of said comparators whereby theresponse of the individual switches in controlled by a selectedcomparator.

10. The combination of claim 7 adapted for use in an elevator systemcomprising a structure giving it to at least two landings. a car mountedfor movement relative to the struc ture to serve the landings. andregulating means for regulating the speed of the car in response to thespeed control signal appearing at the output of the summing circuit.said first control signal source generating a course speed controlsignal. while said second control signal source generates a fine s eedcontrol signal. and actuating means responsive to the approach of a carto a landing at which it is to stop to actuate said second functiongenerator to initiate switching from said course speed control signal tosaid fine speed control signal.

ll. The combination of claim wherein the course speed control signal isa time dependent signal and the fine control signal is a function of thedistance to the fioor at which the car is to stop.

l2. A method of operating a first switch having an open circuitcondition and a closed circuit condition from being predominately in afirst one of said conditions to being predominately in a second one ofsaid conditions. comprising the steps of: generating a repetitivefunction, generating a ramp function when it is desired to operate saidfirst switch. said ramp function having minimum and maximum values whichare less than, and greater than, the respective minimum and maximumvalues of the repetitive function, comparing the repetitive and rampfunctions, operating said first switch repeatedly between said firstcondition and said second condition in response to the instantaneousvalue of the repetitive function exceeding and dropping below theinstantaneous value of the ramp function, with the interval that saidswitch remains in each condition being varied according to thetransition time of the ramp function, so that initially it remainslonger in said first condition and then progressively less in said firstcondition and longer in said second condition until it remainspredominately in said second condition.

13. The method of claim 12 adapted for switching between a first signalsource controlled by said first switch and a second signal sourcecontrolled by asecond switch similar to said first switch including theadditional step of operating said second switch between its open circuitcondition and its closed circuit condition in opposition to said firstswitch.

14. A method of operating a switch having an open circuit condition anda closed circuit condition from being predominately in a first one ofsaid conditions to being predominately in a second one of saidconditions comprising the steps of generating a repetitive waveform,generating a transition waveform which transitions between a minimumvalue which is less than the minimum value of the repetitive waveformand a maximum value which exceeds that of said repetitive waveform,comparing the instantaneous values of the two waveforms, operating saidswitch to said first condition when the instantaneous value of a firstone of said waveforms exceeds that of said other waveform and operatingsaid switch to said second condition when the instantaneous value ofsaid first waveform is less than that of said other wavefonn.

15. The method of claim [4 adapted for switching between a plurality ofsignal sources controlled by switches similar to said switch includingthe steps of generating a transition waveform for each transfer betweensignal sources desired, selecting the pair of signal sources betweenwhich the transfer is to be made, operating a first switch controlling afirst one of the selected signal sources to said first condition whenthe instantaneous value of the associated transition waveform exceedsthat of said repetitive waveform, operating said first switch to saidsecond condition when the instantaneous value of the associatedtransition waveform is less than that of the repetitive waveform andoperating a second switch controlling the second one of the selectedsignal sources between its first and second conditions in opposition tosaid first switch.

. Q Q Q U

1. A switching device comprising a switch having an input terminal andan output terminal, said switch being operative between a firstcondition wherein a circuit is completed between the input terminal andthe output terminal and a second condition wherein no circuit iscompleted between the terminals, and control means for operating saidswitch between said first and second conditions including meansoperative to rapidly and repetitively operate the switch between saidfirst and second conditions with said switch initially remaining in onecondition longer than the other and then progressively less in the onecondition and longer in the other condition until the switch remains inthe other condition substantially continuously.
 2. The device of claim 1including a summing circuit operative to produce an output signal whichis a combination of the signals applied to the summing circuit, a firstsignal source connected to said summing circuit, a second signal sourceconnected to the input of said switch and means connecting the output ofsaid switch to said summing circuit whereby the signal generated by thesecond signal source can gradually be added to or removed from thesignal appearing at the output of the summing circuit through theoperation of said control means to operate said switch from beingpredominantly in one condition to being predominantly in the othercondition.
 3. The device of claim 1 wherein said control means comprisesa first function generator operative to generate a repetitive signal, asecond function generator operative to generate a second signal having atime constant which exceeds the period of oscillation of said firstsignal, and a comparator for comparing the instantaneous values of thesignals generated by said function generators and having a first outputwhen the instantaneous value of a first one of said signals exceeds theinstantaneous value of the other and having a second output when theinstantaneous value of the other signal exceeds that of said one signal,said switch being operative to one condition in response to the firstoutput of said comparator and operative to said other condition inresponse to said second output.
 4. The device of claim 3 wherein asignal generated by said first function generator is substantially asawtooth signal wherein the signals generated by the second functiongenerator is substantially a ramp function, the minimum value of saidramp function being less than the minimum value of said sawtoothfunction while the maximum value of the ramp function exceeds that ofsaid sawtooth function whereby the output of the comparator andtherefore the condition of the switch will remain constant except whilesaid ramp function generator is transitioning between its peak values.5. The device of claim 1 including a second switch which Is operativebetween a first condition wherein a circuit is completed between aninput terminal and an output terminal and a second condition wherein nocircuit is completed between the terminals, and wherein the controlmeans includes coupling means operative to operate said second switchbetween said first and second conditions in opposition to the operationof said first switch between said first and second conditions whereby assaid first switch is operated from being predominantly in said onecondition to being predominantly in the other condition, said secondswitch is operated from being predominantly in said other condition tobeing predominantly in said one condition.
 6. The device of claim 5wherein said control means comprises a first function generatoroperative to generate the repetitive waveform, a second functiongenerator operative to generate a second waveform having a time constantwhich exceeds the period of oscillation of said first waveform, and acomparator for comparing the instantaneous values of the first andsecond waveforms and having a first output when the instantaneous valueof one waveform exceeds that of said other waveform and having a secondoutput when the instantaneous value of said other waveform exceeds thatof said one waveform, said first switch being operative to said firstcondition in response to one output of said comparator and beingoperative to said second condition in response to the other output ofsaid comparator while said coupling means operates said second switch tosaid second condition in response to said one output of said comparatorand operates it to said first condition in response to the other outputof said comparator.
 7. The device of claim 6 adapted for use in acontrol system wherein the second waveform is essentially a rampfunction with a minimum value which is less than the minimum value ofsaid repetitive waveform and a maximum value which exceeds the maximumvalue of the repetitive waveform and including a first control signalsource connected to the input terminal of said first switch, a secondcontrol signal source connected to the input terminal of said secondswitch, and a summing circuit connected to the outputs of said switcheswhereby the control signal appearing at the output of the summingcircuit is one control signal or the other while the ramp function is atits maximum or minimum value and is progressively switched from onecontrol signal to the other as the ramp function transitions from onepeak value to the other.
 8. The combination of claim 7 including a thirdswitch operative between a first condition wherein a circuit iscompleted between an input terminal and an output terminal and a secondcondition wherein no circuit is completed between the terminals, a thirdcontrol signal source connected to the input of said third switch theoutput of said third switch being connected to the summing circuit, anadditional second function generator operative to generate a waveformhaving a time constant which exceeds the period of oscillation of saidfirst waveform, an additional comparator connected to the first functiongenerator and the additional second function generator and having afirst output when the value of one of these waveforms exceeds that ofthe other and having a second output when the value of the otherwaveform exceeds that of said one waveform, the condition of said secondand third switches being responsive to the output of said additionalcomparator, additional coupling means for operating said second andthird switches in opposition to each other in response to the output ofsaid additional comparator and actuating means operative to selectivelyactuate a selected second function generator to initiate a switchingfrom one control signal to another.
 9. The combination of claim 8including gates between the comparators and the respective switches towhich they are connected, said actuating means also including means foractuating said gates to control the response of said sWitches to theoutputs of said comparators whereby the response of the individualswitches is controlled by a selected comparator.
 10. The combination ofclaim 7 adapted for use in an elevator system comprising a structuregiving it to at least two landings, a car mounted for movement relativeto the structure to serve the landings, and regulating means forregulating the speed of the car in response to the speed control signalappearing at the output of the summing circuit, said first controlsignal source generating a course speed control signal, while saidsecond control signal source generates a fine speed control signal, andactuating means responsive to the approach of a car to a landing atwhich it is to stop to actuate said second function generator toinitiate switching from said course speed control signal to said finespeed control signal.
 11. The combination of claim 10 wherein the coursespeed control signal is a time dependent signal and the fine controlsignal is a function of the distance to the floor at which the car is tostop.
 12. A method of operating a first switch having an open circuitcondition and a closed circuit condition from being predominately in afirst one of said conditions to being predominately in a second one ofsaid conditions, comprising the steps of: generating a repetitivefunction, generating a ramp function when it is desired to operate saidfirst switch, said ramp function having minimum and maximum values whichare less than, and greater than, the respective minimum and maximumvalues of the repetitive function, comparing the repetitive and rampfunctions, operating said first switch repeatedly between said firstcondition and said second condition in response to the instantaneousvalue of the repetitive function exceeding and dropping below theinstantaneous value of the ramp function, with the interval that saidswitch remains in each condition being varied according to thetransition time of the ramp function, so that initially it remainslonger in said first condition and then progressively less in said firstcondition and longer in said second condition until it remainspredominately in said second condition.
 13. The method of claim 12adapted for switching between a first signal source controlled by saidfirst switch and a second signal source controlled by a second switchsimilar to said first switch including the additional step of operatingsaid second switch between its open circuit condition and its closedcircuit condition in opposition to said first switch.
 14. A method ofoperating a switch having an open circuit condition and a closed circuitcondition from being predominately in a first one of said conditions tobeing predominately in a second one of said conditions comprising thesteps of generating a repetitive waveform, generating a transitionwaveform which transitions between a minimum value which is less thanthe minimum value of the repetitive waveform and a maximum value whichexceeds that of said repetitive waveform, comparing the instantaneousvalues of the two waveforms, operating said switch to said firstcondition when the instantaneous value of a first one of said waveformsexceeds that of said other waveform and operating said switch to saidsecond condition when the instantaneous value of said first waveform isless than that of said other waveform.
 15. The method of claim 14adapted for switching between a plurality of signal sources controlledby switches similar to said switch including the steps of generating atransition waveform for each transfer between signal sources desired,selecting the pair of signal sources between which the transfer is to bemade, operating a first switch controlling a first one of the selectedsignal sources to said first condition when the instantaneous value ofthe associated transition waveform exceeds that of said repetitivewaveform, operating said first switch to said second condition when theinstantaneous value of the associated transition waveform iS less thanthat of the repetitive waveform and operating a second switchcontrolling the second one of the selected signal sources between itsfirst and second conditions in opposition to said first switch.